We investigated the social effects of the removal of two adult females, including the founder of a matriline, in a group of captive Campbell's monkeys (Cercopithecus campbelli campbelli). Their social behaviour was recorded 1 month before, 1 week after, and 7 months after the removal of the females. Before removal, social interactions occurred mainly within matrilines. Immediately following removal, however, social interactions, and play in particular, increased among matrilines and this increase was still present 7 months later. The role of the younger individuals was important in this increase of play among matrilines. Moreover, following removal, the members of the disturbed matriline were aggressed more by members of the other matriline.